This invention relates to a built-in resistor for cathode-ray tube, which is adapted to be employed for a cathode-ray tube such as a color cathode-ray tube, and also related to a cathode-ray tube housing this built-in resistor.
The loading of voltage to a convergence electrode or focus electrode to be employed in an electronic tube such as a color cathode-ray tube for color television receiver has been conducted by dividing an anode voltage by means of a voltage dividing resistor.
FIGS. 1 to 3 illustrate a conventional voltage dividing resistor, wherein FIG. 1 is a plan view thereof, FIG. 2 is a cross-sectional view taken along the line IIxe2x80x94II of FIG. 1, and FIG. 3 is an enlarged partial view of FIG. 1.
Referring to FIGS. 1 to 3, on one main surface 21a of an insulating substrate 21 made mainly of aluminum oxide, there are arranged five terminal electrode layers 22A to 22E which are formed by the steps of printing an electrode material comprising metal oxides including ruthenium oxide and lead borosilicate glass, drying and baking the printed layer. A predetermined pattern of a resistance layer 23 is formed so as to interconnect these terminal electrode layers 22A to 22E with each other.
This resistance layer 23 is formed by a process wherein a resistance material comprising metal oxides including ruthenium oxide and lead borosilicate glass is printed on the main surface 21a in such a pattern that enables to obtain a predetermined resistance value, and the resultant layer is subsequently dried and baked. This resistance layer 23 is subsequently covered with an insulating covering layer 24a. 
In the regions of the insulating substrate 21 where these terminal electrode layers 22A to 22E are located, there are formed through-holes 25 penetrating from the main surface 21a of the substrate to the other main surface 21b of the substrate. These terminal electrode layers 22A to 22E are electrically connected with terminals 26A to 26E, respectively. One end of each of these terminals 26A to 26E is respectively caulked to the corresponding through-hole 25.
Namely, as shown in FIG. 3, one end of each of terminals 26A to 26E is constituted by a cylindrical portion 26a and a flange portion 26b, wherein the cylindrical portion 26a is inserted into the through-hole 25 and the distal end portion of the cylindrical portion 26a is caulked and fixed to the other main surface 21b of the substrate.
By the way, these terminals 26A to 26E are generally formed of a non-magnetic alloy such as non-magnetic stainless steel (Fexe2x80x94Nixe2x80x94Cr-based alloy) so as not to badly affect the magnetic field to be generated by a deflection yoke (not shown). By the way, this expression of xe2x80x9cnon-magneticxe2x80x9d means, as far as this technical field is concerned, that the relative permeability of material is not more than 1.01, more preferably not more than 1.005.
The caulked portion 26c of the terminal is usually covered with an insulating covering layer 24b in order to suppress any abnormal discharge that might be derived from a potential difference between this caulked portion 26c and the inner wall of the neck portion of cathode-ray tube (not shown).
This insulating covering layer 24b is demanded to have features that it is excellent in heat-resistance so as to withstand against the heating process in the manufacturing process of cathode-ray tube, it is minimal in gas releasability so as not to badly affect the vacuum inside the tube, and it is minimal also in difference in thermal expansion coefficient relative to the insulating substrate. In view of these demands, this insulating covering layer 24b is generally formed of a lead borosilicate glass.
However, since the thermal expansion coefficient of these terminals 26A to 26E made of a non-magnetic alloy is approximately three times as high as that of the insulating substrate or insulating covering layers, cracks are caused to generate in a region of the insulating covering layer 24b which is located in the vicinity of the caulked portion 26c of each of the terminals 26A to 26E, thereby raising a problem that a piece of the insulating covering layer is peeled away and falls from this caulked portion.
If this caulked portion is exposed in this manner, an abnormal discharge may be more likely to be generated, and furthermore, if this peeled piece of the insulating covering layer is adhered to the electron gun or to the inner wall of the neck portion, the withstand voltage property of these members would be deteriorated. Additionally, if this peeled piece of the insulating covering layer is adhered to the apertures of the shadow mask, the clogging thereof would be resulted, thereby giving rise to the deterioration of the yield of cathode-ray tube.
Whereas, if these terminals are formed by making use of an alloy such as covar (Fexe2x80x94Nixe2x80x94Co alloy) or a 42 alloy (42%Fexe2x80x94Ni alloy), the aforementioned problem of the peeling of the insulating covering layer may be suppressed, since the thermal expansion coefficient of the layer made from these alloys can be made almost identical with the thermal expansion coefficient of the insulating covering layer. However, since these alloys are magnetic alloys exhibiting a high permeability, the magnetic field generated from the deflection yoke would be distorted, thereby raising a problem of generating a defective picture image.
This invention has been made in view of the aforementioned technical problems, and hence, an object of this invention is to provide a resistor for cathode-ray tube which is capable of inhibiting the generation of abnormal discharge at the terminal portion and also capable of inhibiting the peel-off of the insulating covering layer, thereby enabling the cathode-ray tube to display a picture image of high quality.
Another object of this invention is to provide a cathode-ray tube which is provided therein with a resistor which is capable of inhibiting the generation of abnormal discharge at the terminal portion and also capable of inhibiting the peel-off of the insulating covering layer, thereby enabling the cathode-ray tube to display a picture image of excellent quality.
According to this invention, there is provided a built-in resistor for cathode-ray tube which comprises an insulating substrate, a resistance layer formed on one main surface of the insulating substrate, a plurality of terminal electrodes mounted on the resistance layer, and a plurality of terminals connected respectively with the terminal electrodes; wherein the plurality of terminals are individually constituted by a base body comprising a non-magnetic alloy, and by a surface layer which is formed on the surface of the base body and comprising an oxide of the non-magnetic alloy, the plurality of terminals have a relative permeability of not more than 1.005, and the surface layer of each of the plurality of terminals is partially provided with an insulating covering layer.
According to this invention, there is further provided a cathode-ray tube comprising an envelope constituted by a panel portion having a fluorescent screen formed on an inner surface thereof and by a funnel portion having a neck portion; and an electron gun disposed inside the neck portion and comprising a cathode assembly, a plurality of grid electrodes, and a resistor for loading a divided partial voltage on the plurality of grid electrodes; which is featured in that the resistor comprises an insulating substrate, a resistance layer formed on one main surface of the insulating substrate, a plurality of terminal electrodes mounted on the resistance layer, and a plurality of terminals connected respectively with the terminal electrodes; the plurality of terminals being individually constituted by a base body comprising a non-magnetic alloy, and by a surface layer formed on the surface of the base body and comprising an oxide of the non-magnetic alloy; wherein the plurality of terminals have a relative permeability of not more than 1.005, and the surface layer of each of the plurality of terminals is partially provided with an insulating covering layer.
As explained above, this invention is featured in that the terminals of the resistor is constituted by a non-magnetic alloy, that the surface layer of the terminals is constituted by an oxide of the non-magnetic alloy, and that the relative permeability of the terminals as a whole is controlled to not more than 1.005.
Preferably, the surface layer of the terminals is formed of an oxide layer that can be obtained through the oxidation of the surface of the base body made of a non-magnetic alloy. As a result, it becomes possible to obtain a surface layer exhibiting an excellent adhesivity.
The non-magnetic alloy constituting the base body of the terminals should preferably be Nixe2x80x94Cr-based alloy. Therefore, the surface layer should preferably be formed of a material comprising, as a main component, Cr2O3 and NiCr2O4 that can be obtained through an oxidation of the surface of the base body made of Nixe2x80x94Cr-based alloy.
The aforementioned surface layer comprising, as a main component, Cr2O3 and NiCr2O4 can be formed through a selective oxidation of the surface of the base body made of Nixe2x80x94Cr-based alloy, i.e. through an oxidation treatment under a condition where the formation of nickel oxide or NiO can be suppressed. The condition for such a selective oxidation may be such that the surface is at first heat-treated at a temperature of 980 to 1100xc2x0 C. in a reducing atmosphere and then, heat-treated at a temperature of 950 to 1050xc2x0 C. in an oxidizing atmosphere.
When the heat treatment in an oxidizing atmosphere is performed at a temperature of less than 950xc2x0 C., the processing becomes too slow to apply it to a practical use. On the hand, when the temperature of this heat treatment is higher than 1050xc2x0 C., it becomes difficult to effectively perform the selective oxidation.
The reducing atmosphere may be an atmosphere containing hydrogen for instance, while the oxidizing atmosphere may be an atmosphere containing water vapor.
The surface layer should preferably be formed of a material containing Cr2O3 and NiCr2O4 at a ratio of 60% by weight or more, more preferably 90% by weight or more. The thickness of the surface layer should preferably be in the range of 0.5 to 2 xcexcm, most preferably about 1 xcexcm.
The surface layer obtained through the aforementioned selective oxidation is suitable for enhancing the adhesive strength thereof with an insulating covering layer to be deposited thereon. Therefore, even if cracks are generated in the insulating covering layer due to a difference in thermal expansion coefficient between the terminals and the insulating covering layer, it is possible to prohibit the insulating covering layer from being peeled away. Therefore, the terminals can be prevented from being exposed through this insulating covering layer, thereby making it possible to suppress the generation of abnormal discharge and also to suppress the deterioration of yield that might be caused by the peeling-off of the insulating covering layer.
Further, even if the surface of the terminals is constituted by an oxide surface layer, the relative permeability of the terminals as whole can be controlled to not more than 1.005, i.e. a value which makes it possible to prevent the generation of distortion in a magnetic field generated by the deflection yoke. Therefore, when this resistor is incorporated in a cathode-ray tube, a picture image excellent in quality can be obtained.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.